Average scattered field from a random PEC cylinder buried below a slightly rough surface

Scattering from a perfect electric conducting cylinder with random radius buried below a half space dielectric homogenous interface is studied. The cylindrical wave scattered by cylinder is expanded in terms of plane wave spectrum. Small perturbation method is used to study the interaction of each plane wave with the interface. The zeroth order term yields solution for a flat interface, whereas scattering from a rough surface is given by first-order term. Results are obtained for both TM and TE polarizations. Analytical expressions of the average scattered field are obtained and verified using numerical evaluation. Different scattering scenarios are simulated by varying the distribution of the radius. It is observed that average scattering cross section of an ensemble with normal/uniform distribution is almost equal to that of a cylinder with mean radius.     

Numerical calculation of the correlation moments of the sound field scattered by a rough surface

Numerically calculated two-dimensional correlation moments of the surface-scattered sound field are presented in the form of correlation surfaces and analyzed. The models of three-dimensional anisotropic and two-dimensional quasi-harmonic surface waves are considered. Data are presented on the angular dependence of the space-time correlation domains of the scattered sound field for receivers spaced across the propagation path in both horizontal and vertical directions, as well as on the shapes of the time-frequency and space-frequency correlation domains.     

Speckle correlations in the light scattered from a weakly rough one-dimensional random metal surface

Perturbation theory is used to compute the angular-intensity correlation function C(q, k|q(?), k(?)) = ?[I(q|k) - ?I(q|k)?][I(q(?)|k(?)) - ?I(q(?)|k(?))]? for p-polarized light scattered from a weakly rough, one-dimensional random metal surface. I(q|k) is the squared modulus of the scattering matrix for the system, and q , q(?) and k , k(?) are the projections on the mean scattering surface of the wave vectors of the scattered and the incident light, respectively. Contributions to C include (a) short-range memory effect and time-reversed memory effect terms, C((1)) ; (b) an additional short-range term of comparable magnitude C((10)) ; (c) a long-range term C((2)) ; (d) an infinite-range term C((3)) ; and (e) a new term C((1.5)) that along with C((2)) displays peaks associated with the excitation of surface polaritons. These new features arise when the factorization approximation is not made in calculating the correlation function C .     

Fourth moments of acoustic waves forward scattered by a rough ocean surface

Abstract

Three types of statistical fourth moments of acoustic waves forward scattered by a randomly rough ocean surface are derived and numerically evaluated. The first one is related to the scintillation index which characterizes intensity fluctuations. The second one is the two-position intensity correlation function which describes the spatial correlation of wave intensity. The third is the fourth-moment two-position coherence function which carries information on the phase fluctuations of the scattered wave. In the range of weak scattering, the ratio of the absolute value of the fourth-moment two-position coherence function over the two-position intensity correlation exactly describes the mean-square fluctuation of the relative phase between the two positions. The acoustic frequency is high so that the Kirchhoff approximation can be used. Two types of spectral functions for surface-height fluctuations are considered: a Gaussian spectrum and the Donelan-Pierson spectrum. The latter is obtained from a model for the fluctuations of the ocean surface height which are controlled by the wind speed at the ocean surface.     

Fourth moments of acoustic waves forward scattered by a rough ocean surface

Three types of statistical fourth moments of acoustic waves forward scattered by a randomly rough ocean surface are derived and numerically evaluated. The first one is related to the scintillation index which characterizes intensity fluctuations. The second one is the two-position intensity correlation function which describes the spatial correlation of wave intensity. The third is the fourth-moment two-position coherence function which carries information on the phase fluctuations of the scattered wave. In the range of weak scattering, the ratio of the absolute value of the fourth-moment two-position coherence function over the two-position intensity correlation exactly describes the mean-square fluctuation of the relative phase between the two positions. The acoustic frequency is high so that the Kirchhoff approximation can be used. Two types of spectral functions for surface-height fluctuations are considered: a Gaussian spectrum and the Donelan-Pierson spectrum. The latter is obtained from a model for the fluctuations of the ocean surface height which are controlled by the wind speed at the ocean surface.     

Travel-time statistics for signals scattered at a rough surface

Abstract

The travel time of signals reflected or refracted by a rough surface is investigated in the geometrical optics approximation. It is shown that surface roughness typically decreases the mean travel time in the case of large-scale roughness, when only one specularly reflecting point moves randomly around its unperturbed position, resulting in a negative travel-time bias (toward early echoes). In the opposite limiting case of multipath propagation, when many specular points exist on a random surface, the travel-time bias is always positive. General results are illustrated by two examples related to ocean remote sensing which involve sound scattering from the ocean surface and bottom.     

Difference scattering field properties between periodic defect particles and three-dimensional slightly rough optical surface

Based on the practical situation of nondestructive examination, the calculation model of the composite scattering is established by using a three-dimensional half-space finite difference time domain, and the Monte Carlo method is used to solve the problem of the optical surface with roughness in the proposed scheme. Moreover, the defect particles are observed as periodic particles for a more complex situation. In order to obtain the scattering contribution of defects inside the optical surface, a difference radar cross section is added into the model to analyze the selected calculations on the effects of numbers, separation distances, different depths and different materials of defects. The effects of different incident angles are also discussed. The numerical results are analyzed in detail to demonstrate the best position to find the defects in the optical surface by detecting in steps of a fixed degree for the incident angle.     

Measurements of light scattering by a characterized random rough surface

Measurements are presented of the angular distribution of four wavelengths of light scattered by a one-dimensional random rough surface, whose probability density function is Gaussian with a standard deviation σ=1.22±0.02 μm and whose lateral correlation function is also Gaussian with 1/e width τ=3.17±0.07 μm. The wavelengths used are 0.63, 1.15, 3.39 and 10.6 μm. The surface is used in two forms: coated with gold and as an almost lossless dielectric. The results are compared to those predicted by a double scattering form of the Kirchhoff formulation. Agreement is good at small angles of incidence but less good at larger angles of incidence.     

Measurements of light scattering by a characterized random rough surface

Abstract

Measurements are presented of the angular distribution of four wavelengths of light scattered by a one-dimensional random rough surface, whose probability density function is Gaussian with a standard deviation σ=1.22±0.02 μm and whose lateral correlation function is also Gaussian with 1/e width τ=3.17±0.07 μm. The wavelengths used are 0.63, 1.15, 3.39 and 10.6 μm. The surface is used in two forms: coated with gold and as an almost lossless dielectric. The results are compared to those predicted by a double scattering form of the Kirchhoff formulation. Agreement is good at small angles of incidence but less good at larger angles of incidence.     

Mirror and antimirror components of scattered field for highly rough surface modeled by system of open flat waveguides

An approximation of physical optics is used to examine plane-wave reflection from a randomly rough surface with large and very abrupt inhomogeneities in the form of a system of open flat waveguides with random parameters. It is shown that for these surfaces, backscattering in the antimirror direction is comparable with scattering in the mirror direction.Small Specialized Enterprise Grot, Institute of General Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 8, pp. 671–677, August, 1992.     

Mass operator for wave scattering from a slightly random surface

This paper deals with the mass operator representing multiple-scattering effects in the theory of wave scattering from a slightly random surface. By means of the stochastic-functional approach, a recurrence equation for the mass operator is obtained in the form of an iterative integral. However, its solution oscillates in a non-physical manner against the number of iterations. Next, the recurrence equation may be regarded as a nonlinear integral equation, when the number of iterations goes to infinity. An analytical solution of the nonlinear integral equation is presented for a special case in which the roughness spectrum is the Dirac delta function. Then, the nonlinear integral equation is solved numerically for the Gaussian roughness spectrum by iteration, starting from such an analytical solution. It is shown that only a few iterations are required to obtain the mass operator, even when the correlation distance is small. Effects of the mass operators on the coherent reflection coefficient and the incoherent scattering cross section are calculated and shown in figures.     

Speckle correlations in the light scattered from weakly rough random metal surfaces

Abstract

Diagrammatic perturbation theory and computer simulation methods are used to compute the angular intensity correlation function C(q, k|q′,k′)=([I(q|k) - (I(q|k))] × [I(q′|k′) - (I(q′|k′))]) for p-polarized light scattered from a weakly rough, one-dimensional random metal surface. I(q|k) is the squared modulus of the scattering matrix for the system, and q, q′ and k, k′ are the projections on the mean scattering surface of the wavevectors of the scattered and incident light, respectively. Contributions to C include: (a) short-range memory effect and time-reversed memory effect terms, C ⁽¹⁾; (b) an additional short-range term of comparable magnitude C ⁽¹⁰⁾; (c) a long-range term C ⁽²⁾; (d) an infinite-range term C ⁽³⁾; and (e) a term C ^(1.5) that along with C ⁽²⁾ displays peaks associated with the excitation of surface plasmon polaritons. The diagrammatic methods are also extended to treat the angular intensity correlation function for the scattering of p to p, p to s, s to p, and s to s polarizations of light from a two-dimensional randomly rough surface. These correlations are again described in terms of C ⁽¹⁾, C ⁽¹⁰⁾, C ^(1.5), C ⁽²⁾, and C ⁽³⁾ contributions to C for the two-dimensional surfaces. Short-range memory and time-reversed memory effects are observed in the two-dimensional C ⁽¹⁾ correlations, and peaks associated with the excitation of surface polaritons are observed in the two-dimensional C ^(1.5) and C ⁽²⁾ correlations. Most of the results for the one- and two-dimensional systems are presented for incident electromagnetic plane waves. In addition, results for one-dimensional systems are presented for incident electromagnetic beams of finite width. Some of the results for one-dimensional surfaces are corroborated by means of computer simulation techniques.     

二维导体微粗糙面与其上方金属平板的复合电磁散射研究

研究了二维导体微粗糙面与其上方金属平板复合电磁散射特征.应用互易性原理使求解二次散射场简化为求解包含平板上的极化电流和微粗糙面散射场的积分方程，从而降低了求解难度.应用物理光学近似和微扰法分别求解了平板上的极化电流和粗糙面的电磁散射场，得到了复合散射截面计算公式并进行了数值计算.尤其对该复合模型后向耦合电磁散射结果进行了详细分析和讨论. 关键词： 互易性原理 复合电磁散射 微粗糙面 平板